Summary of Significant Accounting Policies - Additional Information (Detail)				1 Months Ended	12 Months Ended
	Aug. 31, 2025 USD ($)	Aug. 31, 2024 USD ($)	Aug. 31, 2023 USD ($)	Jul. 31, 2025 USD ($)	Sep. 30, 2026 USD ($)	Sep. 30, 2025 USD ($) Segment	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)
Schedule Of Significant Accounting Policies [Line Items]
Cash, cash equivalents, and restricted cash						$ 24,933,000	$ 117,585,000	$ 45,441,000	$ 14,870,000
Cash and cash equivalents						24,683,000	117,335,000
Restricted cash						$ 250,000	250,000
Number of reportable segments | Segment						1
Goodwill impairment	$ 0	$ 0	$ 0
Minimum percentage of likelihood on goodwill impairment	50.00%
Assets held-for-sale				$ 1,000,000
Advertising expenses						$ 17,300,000	15,000,000	13,500,000
Description of uncertain tax position						greater than 50%
Cash proceeds from sale of assets				$ 4,800,000
Derivative maximum payout						$ 5,000,000		5,000,000
Scenario Forecast
Schedule Of Significant Accounting Policies [Line Items]
Derivative maximum receivable					$ 15,000,000
Derivative maximum payout					$ 5,000,000
Financial Products Corporation
Schedule Of Significant Accounting Policies [Line Items]
Delivery and branch expense reduced under weather hedge contract						$ (3,100,000)	7,500,000	12,500,000
Maximum
Schedule Of Significant Accounting Policies [Line Items]
Cash equivalents, highly liquid investments maturity						3 months
Derivative maximum receivable						$ 15,000,000	$ 12,500,000	$ 12,500,000
Maximum | Customer Lists
Schedule Of Significant Accounting Policies [Line Items]
Intangible assets, amortization period						10 years
Maximum | Trade Names
Schedule Of Significant Accounting Policies [Line Items]
Intangible assets, amortization period						20 years
Maximum | Land Improvements
Schedule Of Significant Accounting Policies [Line Items]
Property and equipment, estimated useful lives						20 years
Maximum | Buildings and leasehold improvements
Schedule Of Significant Accounting Policies [Line Items]
Property and equipment, estimated useful lives						30 years
Maximum | Fleet and Other Equipment
Schedule Of Significant Accounting Policies [Line Items]
Property and equipment, estimated useful lives						15 years
Maximum | Tanks and Equipment
Schedule Of Significant Accounting Policies [Line Items]
Property and equipment, estimated useful lives						10 years
Maximum | Furniture, Fixtures and Office Equipment
Schedule Of Significant Accounting Policies [Line Items]
Property and equipment, estimated useful lives						10 years
Minimum | Customer Lists
Schedule Of Significant Accounting Policies [Line Items]
Intangible assets, amortization period						7 years
Minimum | Trade Names
Schedule Of Significant Accounting Policies [Line Items]
Intangible assets, amortization period						3 years
Minimum | Land Improvements
Schedule Of Significant Accounting Policies [Line Items]
Property and equipment, estimated useful lives						10 years
Minimum | Buildings and leasehold improvements
Schedule Of Significant Accounting Policies [Line Items]
Property and equipment, estimated useful lives						5 years
Minimum | Fleet and Other Equipment
Schedule Of Significant Accounting Policies [Line Items]
Property and equipment, estimated useful lives						1 year
Minimum | Tanks and Equipment
Schedule Of Significant Accounting Policies [Line Items]
Property and equipment, estimated useful lives						3 years
Minimum | Furniture, Fixtures and Office Equipment
Schedule Of Significant Accounting Policies [Line Items]
Property and equipment, estimated useful lives						5 years